The present invention relates to conversion circuits for converting interlaced scanning signals to progressive scanning signals, and particularly to a progressive-scan achieving method and apparatus that generate an interpolating signal by the detection of a motion vector.
In order to convert a 2:1-interlaced scanning signal to a progressive scanning signal, it is necessary to alternately interpolate the scanning lines. As one of the interpolation methods, there is a method for progressive-scan achieving conversion of motion-compensation type. As shown in FIG. 2, the scanning lines are interpolated by using the motion vector between frames or fields (see JP-A-6-121289).
The motion vector indicates from where a certain portion of the current picture has moved here of the previous picture, or one frame before the current picture. In the block matching method, the optimum block that is the most similar (namely, of the highest correlation) to the targeted block of the current frame or current field is extracted from the search range of a reference frame or reference field, and the motion vector is detected from the positional relation between the targeted block and the optimum block. Therefore, if a certain object moves in the horizontal direction with a speed of V (number of pixels/field) during a one-field period, the picture one field before is shifted by the estimated amount of movement V, so that a block with the highest correlation between the fields can be obtained (that is, the accumulative addition of the differences between the targeted block and the candidate block of the fields is the smallest).
On the other hand, the display device such as color liquid crystal display (LCD) or plasma display (PDP), as for example shown in FIG. 5, has display picture elements (hereinafter, called pixels) each formed of three RGB light emitting elements (hereinafter, referred to as RGB sub-pixels) arranged in a predetermined order in one direction, or in the horizontal direction (x-direction) as illustrated to form a line and a plurality of those lines further provided in the direction perpendicular to this horizontal line, or in the vertical direction (y-direction). Thus, the display screen is formed to extend in the two-dimensional direction. Use of the three RGB sub-pixels for each pixel makes it possible to display various different colors.
In recent years, this display device has been used to display high-definition characters. A new technology such as sub-pixel font rendering technology has attracted people's attention. This technology handles the RGB sub-pixels as individual monochrome pixels to apparently improve the resolution (for example, see JP-A-2000-155551). The RGB sub-pixels have been treated as one pixel in the conventional depiction, while the recent depiction of characters uses the horizontal sub-pixels to increase the definition in the arrangement direction three times as much (the example shown in FIG. 5 is capable of displaying with three-fold resolution in the horizontal direction). As to the displaying of characters, Microsoft's ClearType has already implemented the so-called sub-pixel depiction.